1. Field of the Invention
This invention relates to a semiconductor device including a fuse element, and more particularly to a semiconductor device with a structure to control the operation of the fuse element by a laser beam irradiation.
2. Description of the Related Art
A large-scale semiconductor memory device, such as a DRAM and a flash memory, or a high-performance semiconductor logic device embedded these devices thereon generally uses a redundancy circuit as means for remedying a circuit with a faulty element. One known method of using or not using the redundancy circuit is to fuse a metal wiring acting as a fuse element provided in a specific part of multilevel wiring by means of, for example, a laser beam irradiation.
A large-scale, high-performance semiconductor device, such as a high-performance logic device or a DRAM device, is required to operate at high speed. Therefore, to achieve a higher speed operation, it is desirable that the delay in the transmission of signals in the multilevel wiring is decreased. Therefore, favorable materials for the multilevel wiring include a metal with a lower resistance than aluminum (Al), such as copper (Cu), and an insulator with a lower permittivity (so-called low-k insulator) than silicon oxide film as an inter-wiring insulator or an interlevel insulator, such as a fluorine-added silicon oxide, methyl-polysiloxane (MSX), hydrogen-silsesquioxane (HSQ), or poly (arylene) ether (PAE). Since these low-permittivity insulators generally have poorer thermal characteristics than that of a silicon oxide, various problems arise when the fuse elements are fused by the laser beam irradiation.
FIGS. 11 and 12 are sectional views of multilevel wiring structures in the prior art. FIG. 11 shows a structure of a multilevel wiring with four levels which, has a fuse element 340F, formed on a silicon substrate 310. A fuse wiring 345F in the fuse element 340F is fused off by a laser beam LB irradiation. A fuse wiring 345F is provided in a part of a fourth-level metal wiring 345, the top level, and connects a memory circuit to a redundancy circuit. In insulators 348, 349 above the fuse wiring 345F, an opening 350F for a laser beam irradiation is made. Here, Cu is used as a metal material for the wirings 315, 325, 335, and 345 and a low-permittivity insulator is used as the interlevel insulators 311, 321, 331, and 341. Therefore, a material for the fuse wiring 345F is also Cu. Use or nonuse of the redundancy circuit is controlled, depending on whether the fuse wiring 345F is fused off or not.
Comparison between the melting points of the wiring metals has shown that Cu has a melting point as high as 1083° C., whereas Al used in the prior art has a melting point of 660° C. Therefore, to fuse Cu, a laser beam with higher energy than that needed to fuse Al has to be irradiated. The low-permittivity interlevel insulator 341 in contact with the fuse wiring 345F has lower heat resistance than that of a silicon oxide used in the prior art. Therefore, when the Cu fuse wiring is fused by the laser beam irradiation, various problems arise as described below.
The fuse element 340F has a structure shown in FIG. 11 and uses Cu as a fuse wiring material and a low-permittivity insulator as the interlevel insulators 311, 321, 331 and 341. Typical problems encountered when the Cu fuse wiring 345F is fused by the laser beam LB irradiation are shown in FIG. 12. Since the melting point of Cu is higher than that of Al as described above, it is necessary to irradiate with a high-energy laser beam LB to heat the Cu fuse wiring 345F to a high temperature and fuse it. This causes problems: (A) the insulator 341 around the fuse wiring deteriorates due to the resulting heat, which leads to a short or an open in the circuit. In addition, with the thermal stress developed at this time, (B) the Cu wiring 345 is deformed, (C) a separation takes place between the Cu wiring 345 and the overlying passivation films 348, 349, or (D) cracks are generated in the passivation films 348, 349. Furthermore, since the mechanical strength of the interlevel insulator 341 in contact with the Cu fuse wiring 345F is low, (E) a crack might be generated in the interlevel insulator 341 just below the fuse wiring 345F and (F) a crack might be generated in the insulator 341 between the fuse wiring 345F and the Cu wirings 345 in the same level. When a crack has generated in the insulator or the passivation film has come off, moisture and oxygen in the air reach the Cu wiring through the crack, which causes the problem of a reliability degradation of the Cu wiring.
Furthermore, since the diffusion of Cu in the insulator is faster than that of Al and the diffusion of Cu in the low-permittivity insulator is faster than in the silicon oxide film, Cu diffuses into the insulator 341 around the fuse element 340F, or in an extreme case, (G) a Cu penetration is formed in the insulator 341. As a result of the diffusion or penetration of Cu into the insulator, the problem of an unintended short circuit or reliability degradation occurs. In addition, the Cu in the fused part does not evaporate completely, but (H) most of the Cu scatters in and around the laser beam irradiation opening 350F. The scattered Cu particles also cause the problem of a reliability degradation of the semiconductor device.
It is, accordingly, an object of the present invention to provide a semiconductor device capable of controlling an operation of a fuse element without fusing the fuse wiring by the laser beam irradiation and a method of manufacturing the semiconductor device.